From the Annals and Magazine of Natural History, 

 Ser. 6. Vol. xii., September 1893. 



On an Abnormal Specimen of ANTEDON EOSACEA. By Herbert 



C. Chadwick. 



Plate XIII. 



Three months ago, while selecting specimens of Antedon rosacea for 

 serial section-cutting from a number which had been forwarded to the 

 Zoological Laboratory of the Owens College by the authorities of the 

 Zoological Station at Naples, my attention was arrested by one to the 

 disk of which a small rounded body was attached. A cursory examina- 

 tion at once showed the specimen to be one of very exceptional inte- 

 rest, and my thanks are due to Prof. Milnes Marshall for permission 

 to examine and describe it. 



The disk (PL XIII. figs. 1 and 2), which measured 7'5 millim. in 

 diameter, bore the usual number of well-developed arms, and with the 

 exception of the displacement of one of the ambulacral grooves, to be 

 more fully described later on, was in all respects quite normal. On 

 its oro-lateral border, however, it bore the body to which allusion has 

 already been made, and which proved to be a supernumerary disk 

 (figs. 1, 2, and 2, s.d.). Roughly spherical in shape and about 3 

 millim. in diameter, it was attached to the normal disk by a sort of 

 stalk, which gradually narrowed from the oral to the aboral surface. 

 Near the centre of its oral surface was a well-developed mouth, fringed 

 with tentacles, from which five ambulacral grooves radiated, just as 

 do those of the disk of a normal Antedon. Of these, four could with 

 little difficulty be traced outwards to the aboral aspect. 



The remaining one (figs. 1 and 3, x) ran along the stalk of attach- 

 ment to the normal disk and joined the ambulacral grooves of the 

 pair of arms nearest to it, immediately after crossing the line of June- 



